Conventionally, an example of a vehicle door latch device as described in Patent Document 1 is known. FIG. 6 is a diagram showing the structure and operation of a vehicle door latch device disclosed in Patent Document 1. The vehicle door latch device includes a latch 91, a pawl 92, and a helical torsion spring 94. The latch 91 is rotatably supported by a housing provided in a vehicle door and receives a striker 90 on the vehicle body. The pawl 92 is rotatably supported by the housing, and can be fitted to the latch 91 so as to limit the rotation of the latch 91. The helical torsion spring 94 always urges the pawl 92 to rotate in a direction to cause the pawl 92 to engage with the latch 91. The housing has a stopper 93, and the pawl 92 is engageable with the pawl 92.
The pawl 92 includes a block-like main body portion 92a and a shaft portion 92b extending from a center portion of the main body portion 92a. The shaft portion 92b is passed through a shaft receiving hole 95 formed in the housing, so that the pawl 92 is rotatably supported by the housing.
The helical torsion spring 94 includes a helical portion 94a, and first and second engaging legs 94b, 94c, which extend radially outward relative to the helical portion 94a. The shaft portion 92b is passed through the helical portion 94a at a position where the shaft portion 92b does not interfere with the housing. The first engaging leg 94b is engaged with the pawl 92, and the second engaging leg 94c is engaged with an engaging portion 96 provided in the housing.
In this manner, the helical portion 94a of the helical torsion spring 94 is mounted about the shaft portion 92b of the pawl 92 so as to be coaxial with the shaft portion 92b, so that the operation reliability of the pawl 92 is improved.
In the vehicle door latch device disclosed in Patent Document 1, when a vehicle door is in an openable state (hereinafter, referred to as “initial state”) and the striker 90 is not meshed with the latch 91, the main body portion 92a of the pawl 92 contacts the stopper 93 at a location marked by sign ∘. At this time, the main body portion 92a receives, through the first engaging leg 94b of the helical torsion spring 94, a force (indicated by thick arrows) that rotates the pawl 92 counterclockwise as viewed in the drawings about a portion that contacts the stopper 93 as a fulcrum. The urging force urges the shaft portion 92b of the pawl 92 toward the latch 91, thereby causing the shaft portion 92b to contact the inner circumferential surface of the shaft receiving hole 95. At this time, the shaft portion 92b receives an urging force (indicated by thin arrows), which is a reactive force against the above described urging force, through the helical portion 94a. In this state, as shown in the left lower part of FIG. 6 in an exaggerated manner, the pawl 92 is arranged at an eccentric position in the shaft receiving hole 95 such that the clearance C between the shaft portion 92b and the inner circumferential surface of the shaft receiving hole 95 is zero at the top, and the clearance C is greater at the bottom.
When the vehicle door is manipulated to be closed, rotation of the latch 91 accompanying the entry of the striker 90 presses the pawl 92 against the latch 91, so that the pawl 92 is rotated clockwise while acting against the urging force of the helical torsion spring 94. The part of the pawl 92 that contacts the latch 91 is indicated by the sign ∘. At this time, the main body portion 92a of the pawl 92 is pressed downward by the latch 91 at the contact position. Also, the urging force (indicated by thin arrows) acting on the shaft portion 92b through the helical portion 94a is greater than the initial state, and the urging force presses the pawl 92 downward. This arranges the pawl 92 eccentrically in the shaft receiving hole 95, such that the clearance C between the shaft portion 92b and the inner circumferential surface of the shaft receiving hole 95 is greater at the top.
Then, when the pawl 92 is released from the latch 91 immediately after a half-meshed state is achieved, where the latch 91 draws in the striker 90 halfway, the pawl 92 is, as in the initial state, arranged at an eccentric position in the shaft receiving hole 95 such that the clearance C between the shaft portion 92b and the inner circumferential surface of the shaft receiving hole 95 is zero at the top, and the clearance C is greater at the bottom.
When the pawl 92 returns to the position of the initial state, the shaft portion 92b, which moves in the shaft receiving hole 95, hits the inner circumferential surface of the shaft receiving hole 95 and produces unnatural hammering noise, which disturbs the user in some cases. Specifically, when the vehicle door is manipulated to be closed, cheap high pitched sound has been observed to be mixed in deep sound, which is normally produced when the vehicle door is closed.
Patent Document 2 discloses one example of known vehicle door latch devices that reduce such hammering noise. In this vehicle door latch device, the shaft portion of pawl is rotatably supported by a cylindrical projecting wall formed on the housing, and the helical portion of the helical torsion spring is held about the projecting wall. In this configuration, since the urging force of the helical portion does not act on the shaft portion, hammering noise due to movement of the shaft portion as described above is not produced. However, to provide the cylindrical projecting wall between the shaft portion and the helical portion, the helical portion needs have a large diameter. This inevitably causes another problem, namely, an increased size of the entire device.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-129809
Patent Document 2: Japanese Registered Utility Model No. 2519638 (FIG. 3)